Use of booth babes is a somewhat different case. I personally don't like that practice, but it seems likely to me that women on tech conferences are assumed to be booth babes because it is so often true (apparently - I haven't studied that). That is, the likelihood of a woman to be at a tech conference an not be a booth babe might be low, so that the expectation is otherwise. That sucks, of course, but the only way I can see to change that is more tech women attending conferences. Or maybe some obvious signs of non-booth-babeness.

Also, did those women really not manage to talk to anyone? That seems odd, given that booth babes are probably also supposed to make people talk to them, and are considered an effective means for that?